Thermally operated bi-metallic electric devices



Sept' 5, 1961 P. wooDHALL ET AL THERMALLY OPERATED BI-METALLIC ELECTRICDEVICES Filed Dec. 18, 1959 2 Sheets-Sheet l Sept. 5, 1961 P. wooDHALL.ET AL THERMALLY OPERATED ISI-METALLIC ELECTRIC DEVICES 2 Sheets-Sheet 2Filed Dec. 18, 1959 ilnit States Patent 2,999,142 THERMALLY OPERATEDBI-METALLIC ELECTRIC DEVICES Philip "lvloodhail Manchester, and KennethHale, Eccles,

England, assignors to The General Electric lCompany Limited, London,England Filed Dec. 18, 1959, Ser. No. 860,473 Claims. (Cl. 2004138) Thisinvention relates to thermally operated bi-metallic electric devices,such as cut out switches, and more particularly, but not exclusively, todevices used as protective means in electrical equipment such aselectric kettles.

According to the present invention a thermally operated bi-metallicdevice, comprises a bi-metallic element, a slave disc mounted adjacentto the element, means to transmit motion or force from the bi-metallicelement to the slave disc, the slave disc being so `arranged as toresist the motion of force transmitted -from the bi-metallic element,and electric contact means including a pair of concentrically arrangedcontacts in a unitary assembly, the outer of the terminal contactsengaging the periphery of the slave disc and the inner terminal contactbeing adapted to make and break contact with a central contact portionof the slave disc.

Means may be provided for adjusting and setting the temperature at whichthe bi-metallic element operates, and the means may comprise aninternally threaded portion surrounding the threaded periphery of theouter of the two concentrically arranged terminal contacts, in whichportion the terminal assembly may be rotated to give simultaneouslongitudinal adjustment of the terminal contacts.

The thermally operated bi-metallic device may be provided with manuallyoperable reset means which may comprise a sleeve arranged to be slidover the outside of the device and to engage with a projection, or aplurality of projections, from the bi-metallic element.

In order that the invention may be clearly understood one constructionof an electric cut out switch for use in a domestic electric kettle willnow be described by Way of example with reference to FIGURE 1 of theaccompanying drawings which shows a front sectional elevation of theswitch, a modication of this construction will also be described, and isshown partly in section in FIG- URE 2 of the drawings. The device isarranged to tit in a suitable pocket in the head of the immersion heaterof the kettle.

Referring now to FIGURE l, the switch is contained in a switch bodycomprising a spun copper can 1 which holds two porcelain ceramic bodymembers 2, 3 together. The can 1 has a hole 4 in the end face 5 thereofand this hole 4 is covered by a b i-metallic element 6 in the form of adisc situated in a recess 7 in the body member 2 behind the end face ofthe can 1. The body member 2 is centrally apertured and a push rod 8 isplaced in the aperture and arranged in such a manner that it is free tomove in a direction perpendicular to the end face 5 of the can 1. Oneend of this push rod S rests upon the bi-metallic element 6 and itsmovement is a slave movement dependent upon the movement of thebimetallic element.

The other end of the push rod 8, i.e. the end remote from the end face5, is in contact with a spring slave disc 9 made of Phosphor bronze or asimilar spring resilient electrically conducting material, and the disc9 is situated in a cavity in the centre of the switch formed by themember 2 spanning a recess 10 in the member 3. The disc has at itscenter on the side remote from the push rod 8 an electrical contact 11,and on the side adjacent to the push rod there is a small projection 12which is arranged to fit into a recess in the end of the Patented Sept.5, 1961 u dit C push rod 8 and thereby positively locate the slave disc9 with respect to the push rod 8.

The terminal contact assembly of the switch comprises a unitary assemblyof substantially T form with the top portion of the T positioned in therecess 1t) and the shank portion oi the 'l passing through a centrallyarranged aperture in the body member 3. The terminal contact assemblyconsists of an inner terminal contact 13 threaded at its outer-most end1dand with its contact end 15 situated in line With contact 16. Theterminal contact 13 is surrounded by a concentrically arranged outerterminal contact 16 threaded on its outer surface 1'7. The two terminalcontacts are separated by a pair of ceramic insulating bushes It, 19,and these bushes and indeed the whole terminal contact assembly are heldtogether by means of a lock nut 29 screwed on the threaded portion 14;of the terminal contact 13.

The terminal contact assembly is screwed into an internally threadedportion of the switch body in the form of a ring 21 set in the bodymember 3 so that the ends 15, 22 of the contacts 1.3, are disposed inthe recess 1t). The whole assembly 5 is then secured in place in themember' 3 by means of a lock nut 23 on the threaded portion 17 of theterminal contact 16.

In operation the end face 5 of the switch is placed adjacent to aportion of the kettle heating element and under normal conditions thebi-metallic element 6 is in the position shown where it urges thecontact 11 on the slave disc 9 into engagement Iwith the terminal end 1Sof the terminal contact 13, and thereby completing an electric circuitfrom the terminal 13 through the slave disc 9 to the contact end 2.2l ofthe terminal contact `16. The edges of the slave disc 9 rest on theContact end 22, the

t slave disc is under tension due to the force exerted thereupon by thebi-metallic element 6.

When the kettle heating element reaches a temperature higher than normalthe bi-metallic element 6 snaps over in a direction towards the kettleelement and since its force on the slave disc 9 is released and due tothe resilient nature of this slave disc, the disc assumes its morenatural untensioned position and the contact 11 separates from theContact end 15 thereby breaking the electrical circuit.

To set the switch to operate at the correct temperature the end face 5is placed iiat on a metal plate which is at the correct temperature andthe bi-metallic element 6 is allowed to soak in the heat until itattains that temperature. Then, with the lock-nut 23 free, the terminalassembly can be screwed inthe ring 21 in the direction of the end-face 5until the pressure exerted on the bi-metallic element 6 through the pushrod S and the slave disc 9 is suicient to snap-over the bi-metallicelement 6. The lock nut 23 is then tightened up and the switch is set tooperate at the temperature of the soak plate.

The slave disc 9 may be in the form of a bevelled washer, and the set ofthe disc may be such that when the contacts are open not only does thecentral Contact 11 on the terminal 13 separate from the end contact 15but the edges of the slave disc 9 may rest upon the bush 19.

Referring now to FIGURE 2, here a manually operable reset device isincorporated and the bi-metallic disc 6 is provided with two radiallyprojecting ears Z5, one on either side of the disc, which projectthrough holes 26 in the ceramic body member Z and the copper can 1. Theend or the copper can 1 at the end tace 5 is modiiied slightly from thedevice described with reference to FIGURE l inasmuch as the edges of thecan at the hole 4 are turned inwardly to provide a frange 27 upon whichthe disc 6 rests, and which provides a pivot point for the disc when itchanges over from one position to another.

A sleeve 28 is provided around the outside of the can 31 la, and thissleeve has a coiled compression spring Z9 surrounding it and locatedbetween the ears 25 of the disc 6 and a liange member 3d attached to thetop of the sleeve 23. The purpose of the spring 39 is to spring load thesleeve 2S and to keep it clear of the disc 6 during normal conditions.

In the position shown the fbi-metallic switch has operated and haschanged over to open the switch, the reset temperature of the disc isset below the normal ambient so that for the switch to reclos'e itselfthe temperature of the disc will have to be lowered considerably belowthat of normal operating conditions. if this is not possi-ble and whenthe ambient has cooled below the temperature at which the contactsopened pressure can be exerted in a downwards direction on the iiange3%, forcing the ends of the sleeve 2S against the ears Z5 and overcomingthe force of the spring 2.9. Further forcing downwards of the ilange 3Gurges the ears 25 downwards and when they are depressed below the centreline of the disc 6 the disc changes over and closes the contacts oi theswitch. Pressure is then released from the flange 3G and the spring 2.9returns the sleeve Z8 to a natural position resting on the uncompressedspring 29.

it will be appreciated that by incorporating a manual reset device theutility of the switch is increased, since the kettle can be reiilledwith Water after operation of the switch, even though the temperature ofthe water may be higher than the reset temperature of the disc 6,whereas without such a device the kettle could not be used again untilthe temperature of the water had fallen below the ret temperature.

Should the device be reset manually while the temperature of the disc isstill above the operating temperature the switch will re-open againimmediately pressure' is released from the ears, and it does nottherefore impair the safety of a switch to incorporate such a resetdevice.

We claim:

l. A thermally operated bi-metallic device comprising a oi-metallicelement, a slave disc mounted adjacent to the` element, said slave dischaving a peripheral contact portion and a central contact portion, meansto transmit motion or force from the bi-metallic element to the slavedisc, the slave disc being so arranged as to resist the motion or forcetransmitted from the bi-metallic element, and electric Contact meansincluding a pair of concentrically arranged terminal contacts in aunitary assembly, said terminal contacts' being electrically insulatedfrom one another, the outer of the terminal contacts engaging theperipheral contact portion of the slave disc and the inner terminalcontactbeing adapted to make and break contact with the said centralcontact portion of the slave disc.

2. A thermally operated bi-metallic device as claimed in claim l,wherein means are provided for adjusting and setting the temperature atwhich the bi-metallic element operates.

3. A thermally operated bi-metallic device as claimed in claim 2,wherein the adjusting means for adjusting and setting the temperature atwhich the bi-metallic element operates comprises an internally threadedportion surrounding the outer of the two concentrically arrangedterminal contacts and disposed in screw-threaded engagement there-with,in which portion the terminal assembly is rotatably arranged to givesimultaneous longitudinal adjustment of the terminal contacts, and meansfor locking the terminal assembly in an adjusted position.

4. A thermally operated bi-metallic device as claimed in claim l,wherein the device is provided with manually operable reset means.

Y 5. A thermally operated bi-metallic device as claimed in claim 4,wherein the reset means comprises a sleeve slidably arranged over theoutside of the device, said bimetallic element having peripheralprojections arranged to be engaged by said sleeve.

6. A thermally operated switching device comprising a switch body, apair of terminal contacts carried by said body, said contacts beingconcentrically arranged and electrically insulated from one another, aVmovable contact member adapted to bridge said contacts, said movablecontact member comprising ia flexible disc having a peripheral contactportion engaging the outer of said terminal contacts and a centralcontact portion adapted to make and break contact with the inner of saidterminal contacts, a bi-metallic element mounted adjacent to said disc,and means for transmitting a force from the bi-metallic element to thedisc for urging said central contact portion of the disc into engagementwith the inner of said terminal contacts, said disc being resilientlybiased to resist the force transmitted from the bi-metallic eiement.

7. A thermally operated switching device comprising a switch body, aterminal contact assembly carried by said body, said assembly comprisinginner and outer terminal contact members concentrically arranged andelectrically insulated from one another, means for adjusting theposition of said terminal contact assembly Within said body, means forlocking said terminal contact assembly in an adjusted position, amovable contact member adapted to bridge said terminal contact members,said movable contact member comprising a liexible disc having alperipheral contact por-tion engaging the said outer terminal contactmember and a central contact portion adapted to make and break contactwith the said inner terminal contact member, a bi-metallic elementmounted adjacent to said disc, and means for transmitting a force fromthe bi-rnetallic element to the disc, for urging said central contactportion of the disc into engagement with said inner terminal contact,said disc being resiliently biased in accordance with the adjustment ofsaid terminal contact assembly to resist the force transmitted from thebi-metallic element. i

8. A thermally operated switching device comprising a switch body, saidswitch body providing an internally threaded portion, a terminal contactassembly rotatably mounted in said body, said terminal contact assemblycomprising inner and outer terminal contact members concentricallyarranged and electrically insulated from one another and said outerterminal contact member having a threaded external surface disposed inscrewthreaded engagement with said internally threaded portion foradjusting the position of said terminal contact assembly in said body, alocking nut mounted on said outer terminal contact member for lockingsaid assembly in an adjusted position, a movable contact member adaptedto bridge said terminal contact members, said movable contact membercomprising a flexible disc having a peripheral contact portion engagingsaid outer terminal contact member and a ,central contact portionadapted to make and bre contact with said inner terminal contact member,a bi-metallic element mounted adjacent to said disc, and means fortransmitting a force from the bi-metallic element to the disc, forurging said central contact portion of the disc into engagement withsaid inner terminal contact, the disc being resiliently biased inaccordance with the adjustment of said terminal contact assembly toresist the force transmitted from the bi-metallic element.

9. A thermally operated switching device comprising a switch body, asleeve member slidably mounted on said body, a pair of terminal contactscarried by said body, said contacts being concentrically arranged andelectrically insulated from one another, a movable contact memberadapted to bridge said contacts, said movable contact member comprisinga ilexible disc having a peripheralV contact portion engaging the outerof said terminal contacts, a central contact portion adapted to make andbreak contact with the inner of Said terminal contacts, and radiallyprojecting portions arranged to be engaged by said sleeve member, abi-metallic element mounted adjacent to `said disc, and means fortransmitting a force from the ibi-metallic element to the disc forurging said central contact portion into engagement with the inner ofsaid terminal contacts, said disc being resiliently biased to resist theforce transmitted from the bi-metallic element, and Said sleeve memberbeing movable into engagement with said radially projecting portions ofthe disc for exing the disc against its bias for resetting the device.

10. A thermally operated cut-out switch for domestic electricalequipment, comprising a switch body, said switch body providing aninternally threaded portion, a sleeve member slidably mounted on saidbody, a terminal contact assembly rotatably mounted in said body, saidterminal contact assembly comprising inner and outer terminal contactmembers concentrically arranged and electrically insulated from oneanother and said outer terminal contact member having `a threadedexternal surface disposed in screw-threaded engagement with saidinternally threaded portion for adjusting the position of said terminalcontact assembly in said body, a locking nut mounted on said outerterminal contact member for locking said assembly in an adjustedposition, a movable contact member adapted to bridge said terminalcontact members, said movable contact member comprising a 6 flexibledisc having a peripheral contact portion engaging said outer terminalcontact member, a central contact portion adapted to make and breakcontact with said inner terminal contact member, and radially projectingportions arranged to be engaged by said sleeve member, a bi-metallicelement mounted adjacent to said disc, and means for transmitting aforce lfrom the bimetallic element to the disc for urging said centralcontact portion into engagement with said inner terminal contact member,said disc being resiliently biased in accordance with the adjustment ofsaid terminal contact assembly to resist the force transmitted from thebi-metallic element, and said sleeve member being movable intoengagement with said radially projecting portions of the dise forflexing the disc against its bias for resetting the switch.

References Cited in the le of this patent UNITED STATES PATENTS1,823,345 Britt Sept. l5, 1931 2,207,462 Kurtz July 9, 1940 2,230,770Van Almelo Feb. 4, 1941 2,478,503 lRichmond Aug. 9, 1949

